1. Field of the Invention
This invention relates to a keyboard musical instrument having a casing comprising two halves, more particularly to a portable electronic keyboard instrument with the casing made of plastics.
2. Prior Art
Conventional musical instrument of the type under consideration employs a casing comprising molded upper and lower half shells connected together, the shells being made of a suitable synthetic resin. The lower shell has multiple integral sections for mounting associated keys and other components. In order to facilitate the removal of the lower shell from molds, recesses are formed in the outer surface of the lower shell at regions where the integral mounting sections are provided. This detracts much from the appearance of the casing. One method of overcoming this difficulty has been to provide molds designed to form a lower shell having no recess. This procedure has been found not satisfactory, however, in that it increases the manufacturing cost of the lower shell because of added molding material. Another alternative has been to provide a separate cover member designed to be attached to the outer surface of the lower shell to conceal the recesses from view. However, this approach also has been found not satisfactory in that it increases the manufacturing cost of the casing on account of the addition of such a separate cover member.
Conventionally, the lower shell has a battery receiving portion at the rear portion thereof, and therefore the horizontal depth of the casing is increased. Further, the lower shell has an integral stop means for limiting the upward movement of the keys. With this construction, the keys could not easily be mounted on and removed from the lower shell.
There is known another keyboard structure in which each key has a downwardly extending rear end portion which is loosely received in an opening formed through a chassis. A transverse groove is formed in the rear end face of the key and is engaged with the edge of the opening about which the key is pivotally movable. A separate retaining member is secured to the chassis and extends into the opening so that the end of the retaining member is disposed in closely spaced relation to the rear end portion of the key to thereby prevent the transverse groove from becoming disengaged from the opening edge during the operation of the key. This keyboard structure has been found disadvantageous in that it is rather difficult to mount the retaining member on the chassis since the retaining member must be attached to the chassis after the keys are mounted on the chassis. And besides, the separate retaining member is required only for the purpose of retaining the key in position on the chassis. Another keyboard structure is also known in which each key has at its rear end a transverse groove which engages the upper edge of an opening formed through an upwardly extending portion of a chassis. The key has a projection extending downwardly from its rear end, the projection being disposed in closely spaced, opposed relation to the lower edge of the opening so as to prevent the key from becoming disengaged from the opening during the operation of the key. This known keyboard structure has also been found disadvantageous in that the key can not easily be mounted on the chassis because of the presence of the projection.
One known molded key for a keyboard structure for an electronic musical instrument, such as an electronic organ, has an integral L-shaped retaining portion having a first leg extending downwardly from the key body and a second leg extending generally perpendicularly from the first leg at its lower end. The second leg is engageable with an associated chassis to limit the upward movement of the key. The outer surfaces of the first and second legs are disposed in coplanar relation to each other. Also, the inner surfaces of the first and second legs are disposed in coplanar relation. One problem of such a key is that a molding machine for forming the key is complicated in construction because of such an undercut construction. As a result, the key could not be manufactured at low costs.
The prior art keyboards employ a plurality of resilient members operatively associated with juxtaposed keys, respectively, for urging the same into their inoperative or raised position. The mounting of the plurality of resilient members on the keyboard required much time and labor. Further, it is quite difficult to mount the individual resilient members in such a manner that they apply uniform biasing forces to the respective keys. As a result, the touch of the keys is not uniform. Further, during the operation of the keys, stress is directly applied through the respective resilient members to a mounting portion of the frame which supports the resilient members. Therefore, the mounting portion must have a sufficient strength to withstand the stress exerted thereon. As a result, added material was required to increase the strength of the frame or chassis.